This invention relates generally to gas pressure diaphragm regulator valves and particularly to gas pressure diaphragm regulator valves that include a built in pressure relief mechanism.
Gas pressure regulator valves are well known in the art. In such valves, a valve disc or plug and a seat assembly are positioned intermediate an upstream and a downstream portion of a flowpath for controlling downstream pressure and flow by varying the valve opening, that is, the amount by which the disc is displaced from its valve seat. Pressure and flow regulation are achieved by modulating the valve opening to develop the downstream pressure required to deliver the flow demanded by the load. A popular form of regulating valve includes a diaphragm, that acts as both a measuring and a loading device, with the downstream pressure being applied to one side of the diaphragm against the force of an opposed adjustable spring. In the specific type of valve to which the invention is directed, the upstream pressure applies an opening force against the valve disc. The opening force is applied through a stem and linkage mechanism to a pusher post that is in communication with the diaphragm and the regulator spring. The lower downstream pressure applies an opposing force, directly to the diaphragm, that tends to close the valve. The linkage mechanism has a mechanical disadvantage that enables the downstream pressure to offset the force of the regulator spring, which enables regulation.
Valves of this type often incorporate a pitot tube for applying the pressure at the vena contracta to the diaphragm. At the vena contracta, which is generally located a short distance downstream of the actual valve opening, the flow velocity is at a peak and the pressure is at a minimum. The low pressure provides a so-called "velocity boost" due to the reduced pressure applied to the diaphragm and yields well-known operating advantages.
In a pipeline installation, there is always the possibility of a sudden increase in pressure that can pose significant problems for the regulating mechanisms coupled to the line. In a pressure relief diaphragm type regulator, means are provided for rapidly increasing the pressure on the diaphragm to close the valve and protect the load equipment connected to the downstream side. In many installations the regulating valves are not "pressure relieved", but some other mechanism is placed in the pipeline to protect against abnormal pressure increases. As those skilled in the art know, the regulating valve itself can be damaged or even destroyed by the force applied to the diaphragm as a result of a large increase in downstream pressure. Even in pressure relief type diaphragm regulator valves which include a mechanism to relieve the increased downstream pressure, the linkage may be stressed to the point of damage or destruction.
Prior art diaphragm regulator valves include means for limiting the movement of the mechanical linkage that couples the valve plug to the pusher post. The mechanical linkage generally consists of a sheet metal lever, a valve stem and one or more pins, legs and cams for translating motion of the valve stem, which is attached to the valve disc holder, to the pusher post. Linkage movement is halted at a certain point by contact with a rigid stop. The resulting stress on the linkage under these conditions may be considerable and damage or destruction can result.
In diaphragm type regulator valves with built in pressure relief mechanisms, the pusher post and diaphragm are coupled by means of a locking spring which keeps the diaphragm and pusher post in engagement. Under normal pressure conditions, the linkage engages a stop in the lower casing of the valve that prevents the pusher post from traveling beyond a predetermined point. The diaphragm can, however, continue moving against the combined actions of the regulator spring and the locking spring and open a passageway from the lower casing, through the diaphragm structure, to the upper casing, for venting of the excess pressure. As mentioned, the construction has inherent disadvantages, both from a mechanical tolerance point of view and from an operating point of view since the valve stem, lever and connecting pins can easily be damaged during an over pressure condition. It is also important to provide some means for maintenance personnel to determine that an over pressure condition has occurred. It is thus common in the art to provide some form of pressure relief indicator mechanism for visually indicating the occurrence of an increased pressure condition.
One form of prior art pressure relief indicator utilizes a brightly colored indicator ball. The ball is mounted to a small shaft that is secured in the vent opening of a valve by means of a rubber grommet that is fitted to a metal stamping which is pressed, or otherwise secured, in the vent opening. The grommet frictional forces on the stem of the indicator ball mechanism keeps the ball inside the vent against the force of a very light spring. The metal stamping has an opening for relieving pressure inside the spring casing to the atmosphere. Upon operation of the relief mechanism, the relief gas flowing through the opening in the stamping exerts pressure on the ball and drives it out of the vent where it is visible to maintenance personnel. The light conical spring keeps the ball in its outward position to indicate that a pressure relief operation has occurred. The stem has a slightly enlarged end to prevent its withdrawal from the grommet under normal relief operating conditions. Under high pressure conditions, however, the stem may pull through the grommet, resulting in the discharge of the ball and stem mechanism as a projectile. This not only presents a danger from the flying objects, but it negates the function of signalling occurrence of a pressure relief operation. Also the mechanism involves a number of parts that require assembly and is complex and relatively expensive.
Accordingly, there is a need for a diaphragm type regulator valve and a pressure relief indicator that solve these problems of the prior art.